This invention relates broadly to concrete cutting apparatus and, more particularly, pertains to a motor control used in the travel and cutting operations of a multi-directional, carriage-mounted saw for cutting extruded, prestressed concrete slabs.
Concrete slabs are formed on casting beds by extruding machines of the type wherein a frame is mounted on a pair of rails between which a pallet extends. A hopper is mounted on the frame and feeds concrete or the like downwardly to a set of augers which are rotated by a source of power. These augers pick up the concrete and compress it within a packing chamber to form a slab with long bores therethrough formed by the augers. The compression of the concrete drives the machine forwardly on the rails with the slab being extruded therebehind.
Conventional extruding machines are of sufficient dimensions to form slabs in long lengths of 400-600 feet with widths of 4-8 feet and thicknesses of 4-20 inches. Because of their immense mass, these slabs must be cut to a more reasonable size before they can be used in the construction of buildings. Traditionally, construction workers will use various sawing apparatus to make a longitudinal cut or a 90.degree. cross-cut in order to obtain a workable piece of material. After the sawed piece is lifted from the casting bed, such as by a crane or the like, and transported to a remote building site, a road saw or chain is typically used to perform additional cutting or trimming often along an angular orientation to meet the specifications of the building architect.
Efforts to produce concrete slabs in the manner described above create problems in wasted concrete and additional handling of severed concrete slabs. Saws used at the building site must be blocked and braced to make additional cuts, and additional lifting equipment and manpower must be made available, both of which contribute to undesirably high labor and production costs. As more architects design buildings exhibiting predominantly angular features, it is desirable to offer a concrete saw which is able to improve upon the initial cutting operation and reduce the amount of expenditures currently incurred in the formation of concrete building material.
The present invention relates to a concrete saw such as disclosed in copending U.S. patent application Ser. No. 08/864,235, filed May 29, 1997, the disclosure of which is hereby incorporated by reference. In that application, a saw for cutting an extruded prestressed concrete slab having a length, a width and a thickness includes a mobile framework assembly movable along the length of the concrete slab. A first motive system is provided for moving the framework assembly along the concrete slab. A carriage system is rotatably supported from the framework assembly about a first vertical axis substantially perpendicular to the concrete slab and slidably mounted on the framework assembly for movement back and forth across the width of the concrete slab. A second motive system is mounted on the framework assembly for rotating the carriage system relative to the framework assembly. A cutting arrangement including a powered rotary cutter is suspended from the carriage system over the concrete slab. The cutting arrangement is slidable along a longitudinal axis of the carriage system and is movable up and down between the carriage system and the concrete slab along a second vertical axis substantially parallel to the first vertical axis. A third motive system is mounted in the carriage system for moving the cutting arrangement along a longitudinal axis of the carriage system. A fourth motive system is mounted on the framework assembly for moving the carriage system and the cutting arrangement back and forth across the width of the concrete slab. A fifth motive system is provided for mounting the cutting arrangement up and down along the second vertical axis. A sixth motive system is provided for rotating the rotary cutter. The cutter is constructed and arranged to make longitudinal, lateral and angular cuts in a top surface and through the thickness of the concrete slab.
In the use of the aforementioned concrete saw, the first motive system is embodied in a single stage, variable speed, electric gear motor which enables selective positioning or travel of the saw framework assembly along the length of the concrete slab. This first motive system is used in combination with a more powerful electric motor defining the sixth motive system when it is desired to execute a longitudinal or "rip" cut along the length of the concrete bed. In the course of providing such a rip cut the electric gear motor of the first motive system is controlled by a conventional VFD (variable frequency device) allowing the operator to vary the speed of the single stage gear motor during cutting as well as during travelling. Because of the wide range of speed needed (i.e. slow speed for rip cutting and fast speed for travelling), travelling speed was sacrificed for cutting speed. The design of the variable speed gear motor in the first motive system typically provided an optimal travelling speed of 30 ft/min.
While the above described motor control provides a satisfactory arrangement which adequately severs concrete slabs along longitudinal paths, it is desirable to provide a two-stage, variable speed electric gear motor which will allow slow speed for rip cutting and faster speeds (e.g. 100 ft/min.) for travelling. Although the broad concept of utilizing multi-stage electric motors is well known, it is desirable to improve the longitudinal cutting and travelling capability of the concrete saw described in the aforementioned copending patent application.
The present invention advantageously provides a control arrangement for a self-propelled, rail mounted saw for cutting prestressed, hollow-core, extruded concrete slabs along diverse paths in a manner which more efficiently readies the severed concrete material for building application.
It is a primary object of the present invention to provide a motive system for a self-propelled, rail-mounted concrete saw which can be quickly positioned along the length of an extruded concrete slab and operated in conjunction with a rotary cutting element to effect a rip cut regardless of the hardened strength of the concrete. It is also an object of the present invention to provide such a motive system that can be operated in a high speed range and a low speed range. It is a further object of the present invention to provide such a motive system which operates in accordance with the position of the carriage mounted cutting arrangement.
One aspect of the invention relates to a self-propelled concrete saw for cutting a prestressed concrete slab and having a framework assembly movable along the length of the concrete slab, a carriage system movably supported from the framework assembly and a cutting arrangement movably suspended from the carriage system for cutting the concrete slab along a diverse path. The improvement resides in a control arrangement having a first stage enabling the framework assembly to travel at variable speeds over a first range, and a second stage enabling the framework assembly to travel at variable speeds over a second range of speeds less than the first range as the cutting arrangement cuts the concrete slab. The control arrangement includes a two speed electric motor, typically 3 HP/11/2 HP, having a variable speed of 0 to 1750 rpm. The motor is connected by a variable frequency device. The control arrangement is responsive to a vertical position of the cutting arrangement relative to the framework assembly. The cutting arrangement has an upper position spaced vertically above the concrete slab and a lower position in contact with the cutting slab. The control arrangement enables the framework assembly to travel over a first range of variable speeds when the cutting arrangement is in the upper position, and enables the framework assembly to travel over a second range of variable speeds when the cutting arrangement is in the lower position.
In the preferred embodiment, the control arrangement includes a first variable frequency device for controlling the movement of the framework assembly, and a second variable frequency device for controlling the movement of the cutting arrangement relative to the carriage system and the movement of the carriage system and cutting arrangement relative to the width of the concrete slab. The first range of variable speeds is preferably twice the rate of the second range of variable speeds.
In another aspect of the invention, a saw is provided for cutting an extruded, prestressed concrete slab having a length, a width, and a thickness. The saw includes a framework assembly movable along the length of the concrete slab, and first motive system for selectively moving the framework assembly along the concrete slab. A carriage system is rotatably supported from the framework assembly about a first vertical axis perpendicular to the concrete slab and is slidably mounted on the framework assembly for movement back and forth across the width of the concrete slab. A cutting arrangement includes a rotary cutter suspended from the carriage system over the concrete slab and movable up and down along a second vertical axis substantially parallel to the first vertical axis, the cutting arrangement also being slidable along the carriage system. A second motive system is provided for selectively moving the cutting arrangement up and down along the vertical axis so as to bring the rotary cutter into and out of engagement with the concrete slab. A third motive system is provided for selectively moving the rotary cutter once the rotary cutter engages the concrete slab. The control arrangement is interconnected with the first motive system to move the framework assembly to a cutting position along the slab over a first range of speeds with the rotary cutter raised out of engagement with the concrete slab. The concrete arrangement is also operable to move the cutting arrangement into engagement with the concrete slab after which the first and third motive systems are actuated. The first motive system is operated over a second range of variable speeds less than the first range of variable speeds to enable longitudinal cutting of the concrete slab.
In yet another aspect of the invention, a saw is provided for cutting of extruded, prestressed concrete slab having a length, a width, and a thickness. The saw includes a movable framework assembly movable along the length of the concrete slab, and a first motive system for moving the framework assembly along the concrete slab. A second motive system is mounted on the framework assembly for rotating a carriage relative to the framework assembly. The cutting arrangement is selectively engageable with the concrete slab and includes a powered rotary cutter suspended from the carriage system over the concrete slab, the cutting arrangement being slidable along a longitudinal axis of the carriage and movable up and down between the carriage system and the concrete slab along the second vertical axis substantially parallel to the first vertical axis. A third motive system is mounted on the carriage system for moving the cutting arrangement along a longitudinal axis of the carriage system. A fourth motive system is mounted on the framework assembly for moving the carriage system and the cutting arrangement back and forth across the width of the concrete slab. A fifth motive system is provided for mounting the cutting arrangement up and down along the second vertical axis, and the sixth motive system is provided for rotating the rotary cutter. A control arrangement is constructed and arranged for movement of the framework assembly over the first range of speeds when the cutting arrangement is disengaged over the concrete slab, and to allow movement of the framework assembly over a second range of speeds less than the first range of speeds as the cutting arrangement engages the concrete slab. The control arrangement includes a first variable frequency drive connected to the first motive system, and the second variable frequency drive connected to the third and fourth motive systems.
The invention further contemplates a method for cutting a concrete slab. The method comprises the steps of supporting the concrete slab on a casting bed having spaced side rails; mounting a framework assembly for non-steerable movement longitudinally upon the spaced side rails; movably suspending a cutting arrangement from the framework assembly to selectively bring a cutting arrangement into and out of engagement with the concrete slab; moving the framework assembly over a first range of variable speeds while the cutting arrangement is out of engagement with the concrete slab to position the cutting arrangement at a desired cutting position longitudinally of the concrete slab; and moving the framework assembly over a second range of variable speeds less than the first range of variable speeds as the cutting arrangement engages the concrete slab. The method includes the step of movably supporting a carriage from the framework assembly. The step of moving the frame-work assembly includes the step of providing a two-speed variable speed electric motor-brake controlled by a variable frequency device.
Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.